Over the decades, Japan has perfected this monumental work of art, proudly proclaiming that its complex flood prevention system stands on par with the wonders of the world.
Cecilia Tortajada will likely never forget the sensation of stepping down each staircase to visit one of Japan’s masterpieces: the massive water reservoir part of the “flood defense system” that protects Tokyo from storm surges. Upon reaching the bottom of the reservoir, Tortajada was awestruck by the dozens of concrete columns supporting up to 500 tons. The underground reservoir looks nothing short of a “temple dedicated to Greek gods.”
MAOUDC Underground Water Drainage Channel
“You will feel incredibly small,” Tortajada, a water management expert at the Singapore National Policy Institute, remarked. “Tokyo is indeed very well-prepared to cope with flooding.”
This “flood prevention temple” lies 22 meters underground and is officially named the MAOUDC (Metropolitan Area Outer Underground Discharge Channel). The 6.3-kilometer tunnel system was constructed alongside several towering cylindrical water storage shafts, sufficient to help keep Tokyo from flooding.
Japan’s Flood Prevention Efforts
Over the decades, Japan has refined this monumental work of art, taking pride in its sophisticated flood prevention system that rivals world wonders. However, the future remains uncertain as climate and rainfall patterns continue to change.
Japan’s Largest Underground Flood Prevention Facility
Tokyo is located in a floodplain surrounded by five major river systems and dozens of smaller tributaries that swell during each rainy season. Rapid urbanization and industrialization, coupled with uncontrolled groundwater extraction, have caused some areas to sink and gradually fall below sea level.
Although Japan has battled floods for centuries, its current flood prevention system was only truly established after World War II. The 1947 Kathleen storm destroyed approximately 31,000 homes and claimed 1,100 lives. The subsequent Kanogawa storm further devastated the city, submerging thousands of homes and production facilities.
In response to this situation, the Japanese government was determined to take action. “Even in the 1950s and 1960s, when Japan was still recovering from the war, the government allocated 6-7% of the national budget to mitigate disaster risks,” said Miki Inaoka, a disaster expert at the Japan International Cooperation Agency (JICA).
Tokyo now boasts a flood prevention system featuring numerous dams, reservoirs, and levees
At that time, experts and engineers faced many challenging problems. If heavy rain fell upstream, the water flow in the rivers would inundate the central areas downstream. Such rainfall could overwhelm the drainage system, while tidal waves and tsunamis could threaten coastal areas. Everything had to be meticulously calculated to anticipate an earthquake that could break a dam.
After decades of planning and constructing various corresponding structures, Tokyo now proudly possesses a flood prevention system that includes dozens of dams, reservoirs, and levees. Deep underground, a maze of tunnels has also been built alongside numerous subway lines and gas pipelines to serve this century-old project.
MAOUDC – “The Dragon Beneath the Earth”
MAOUDC, valued at $2 billion, is regarded as one of the most impressive engineering feats in Tokyo. Completed in 2016 after 13 years of construction, MAOUDC is the largest flood prevention facility in the world and a testament to the Japanese government’s relentless improvement efforts.
A 70-meter high water reservoir, large enough to contain a space shuttle or the Statue of Liberty
According to the BBC, the underground channel system will siphon water from the smaller rivers in northern Tokyo, which then flows into five massive underground cylindrical reservoirs. Each reservoir is 70 meters tall, large enough to contain a space shuttle or the Statue of Liberty. The water in the reservoirs is then channeled through the 6.3-kilometer tunnel system to the Edo River at a rate of nearly 200 cubic meters per second. Water is discharged into the river through a system of six outlets, each large enough for a subway train to pass through.
To achieve this, MAOUDC relies on the high-pressure pump system of the Showa Pump Station – Japan’s largest pumping station that can drain a standard 25-meter swimming pool in one second. Regarded as the heart of Tokyo’s emergency drainage system, this facility consists of four high-pressure pumps, each capable of discharging 50 cubic meters of water per second with a power of 14,000 horsepower.
“It’s like something out of a science fiction novel,” Inaoka from JICA said.
Japan’s largest pumping system can drain a standard 25-meter swimming pool in one second
However, Inaoka also acknowledged that the continual changes in climate and varying rainfall amounts will challenge Tokyo’s infrastructure, making disaster response planning even more difficult.
According to city data, the underground defense system is designed to withstand rainfall up to 50 mm per hour, especially in densely populated areas. However, data collected over more than 30 years indicates that rainfall patterns are changing. Some experts estimate that in the 21st century, the frequency of rainfall in Japan could increase by 10%-19%.
“The climatic characteristics mean that Japan frequently experiences floods and heavy rainfall,” said Kei Yoshimura, a meteorology professor at the University of Tokyo.
Visitors to MAOUDC
In a book published in 2014, Tsuchiya, Director of the Japan River Research Center, warned that Tokyo is not prepared to handle heavy rainfall due to global warming. Especially in low-lying areas like Tokyo, around 2.5 million residents could be affected by sudden tidal surges.
In early 2018, heavy rains in western Japan resulted in hundreds of fatalities. If such a situation were to occur in Tokyo, the city could suffer tremendous damage.
“If a country as well-prepared as Japan is affected, and a city as well-prepared as Tokyo floods, we should all be on alert,” Cecilia Tortajada remarked.
MAOUDC is set to open for tours during non-operational hours to raise public awareness of the importance of disaster prevention efforts. Thanks to MAOUDC, Tokyo is believed to potentially reduce flood damage in the region by up to 90%.
